Shulou(Shulou.com)06/01 Report--

In the user_objects view, there are two fields, created and timestamp. According to the official manual, created is the creation timestamp of the object, DATE type, timestamp is the object definition timestamp, VARCHAR2 type, and its length is 19, which happens to store "2018-12-27 09:31:14", which obviously has the same meaning as created.

But when we created the table, we found that the time difference between created and timestamp retrieved by user_objects view was 12 hours. Why?

Am, Latin ante meridiem, should be before noon, to be exact.

Pm, Latin post meridiem, should be after noon, to be exact.

About the 12-hour system, let's popularize science.

The twelve-hour system originated in Egypt. However, the length of each hour varies from season to season. 12 hours from dusk to dawn, and 12 hours from dawn to dusk. The Romans also used the 12-hour system: the whole day was divided into twelve hours on average (so the length of the days of the year was different), and the night was divided into three hours. This is because before the invention of the water trap, people used the sun as a timing tool, so there was no way to accurately divide the time.

The Roman count of morning time is the opposite of what it is now: for example, "3 ante meridiem" or "3 hours ante meridiem" means the third hour before noon, rather than the modern meaning "third hour after midnight".

Today, the twelve-hour clock is still the way most pointer clocks display time, rotating once every twelve hours. For a 24-hour rotation, the hour hand rotates only 15 degrees per hour, which is too small to tell.

Although it has been widely replaced by the 24-hour system in the modern world, especially in written communications. However, the ante meridiem/post meridiem form used in the 12-hour system is still the main form of writing and conversation in Australia and the United States. It is also often used with the 24-hour system in Canada (especially Quebec), the Commonwealth, Albania, Greece and other English-speaking areas, as well as in the Spanish-speaking areas of South America. The abbreviations "AM" and "PM" are also often used in English and Spanish. In Albania, the words "PD" and "MD" have the same meaning, and in Greece they are "π μ" and "μ μ". In most other languages, the terms "morning" and "afternoon" are rarely used in formal situations, but the informal 12-hour system is used in folk.

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